1. Field of the Invention
The present invention relates to an aperture-reinforcing device for flexible envelopes intended to be tensioned, and in particular to an aperture-reinforcing device for aerostat envelopes.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings is a general view of a conventional experimental aerostat also known as a xe2x80x9csonde balloonxe2x80x9d.
As can be seen in FIG. 1, an aerostat of this kind typically includes a flexible envelope 1 filled with a gas lighter than air, such as hydrogen or helium.
The envelope comprises a plurality of plastics material film panels 2 welded together in the meridian direction and converging toward a top part 3 of the aerostat referred to as the xe2x80x9cNorth Polexe2x80x9d and toward a bottom part 4 of the aerostat referred to as the xe2x80x9cSouth Polexe2x80x9d.
The panels 2 forming the envelope 1 are conventionally made of polyethylene reinforced with polyester fibers and the polar zones 3, 4 of the envelope 1 include aperture-reinforcing devices 5, 6 consisting either of circular flanges fixed by nuts and bolts or of components glued to the envelope.
The aperture-reinforcing device 6 of the South Pole of the balloon includes a ring 7 adapted to support a flight system 8, typically comprising a basket 9 that can carry scientific instruments, a radar reflector 10 and a parachute 11.
New composite envelope materials have recently been used to improve the strength-to-weight ratio of experimental aerostat envelopes, so that larger payloads can be carried.
For example, new generation envelope open stratosphere balloons have envelopes comprising very thin polyester panels reinforced with carbon fibers or oriented polyethylene fibers.
These extremely light materials unfortunately have the disadvantage of being prone to tearing by shear forces, i.e. forces applied in the direction transverse to the plane of the envelope.
For this reason, conventional aperture-reinforcing devices at the poles are not suitable for the new generation envelopes, because they apply high shear forces to the panels.
An object of the present invention is to provide a pole aperture-reinforcing device suitable for this new type of envelope.
The above object of the invention, and others that will become apparent on reading the following description, are met by an aperture-reinforcing device for flexible envelopes intended to be tensioned, and in particular for aerostat envelopes, the device including adjacent first and second annular members such that the envelope can pass successively over inside parts of surfaces of the first and second annular members, then over an outside part of a surface of the second annular member, and then again over the inside part of the surface of the first annular member, between itself and the part.
According to one feature of the invention the aperture-reinforcing device further includes means for urging the first and second annular members together to immobilize the envelope when it is not tensioned.
According to another feature of the invention a first flange is fixed to the periphery of the first annular member, a second flange is placed over the second annular member, and a plurality of springs is tensioned between the first and second flanges.
According to another feature of the invention a seal is disposed between the second flange and the second annular member to enable sealed closure of the aperture-reinforcing device.
According to another feature of the invention the first and second annular members are toroidal.
Because of the above features, the aperture-reinforcing device according to the invention applies low shear forces to the panels of the envelope in the polar zones.
What is more, an aperture-reinforcing device according to the invention can be made from a small number of components, reducing its mass and its manufacturing cost.
Other features and advantages of the present invention will become apparent on reading the following description and examining the accompanying drawings, wherein like numerals refer to like parts throughout.